Atomistic Mechanisms and Diameter Selection during Nanorod Growth

We study in this paper the atomic mechanisms of nanorod growth and propose the mechanism of diameter selection of nanorods. A characteristic radius is demonstrated to be crucial in nanorod growth. If the critical size of the two-dimensional nucleus is assumed to be 1, the characteristic radius increases proportional to 1/5 power of the ratio of the interlayer hopping rate of adatoms across the monolayer steps to the deposition rate. When the radius of the initial island is larger than this characteristic radius, a screening effect is important for nanorod growth. The growth morphology evolves from a taper-like structure to a nanorod with a radius equal to the characteristic radius after some transient layers, depending on the screening strength. When the radius of the initial island is smaller than this characteristic radius, the nanorod morphology can be maintained during the growth, with the stable radius being limited by both the radius of the initial island and the three-dimensional Ehrlich-Schwoebel barrier. Therefore, different growth modes and the diameter of nanorod can be selected by changing the characteristic radius, via controlling the growth condition. The theoretical predictions are in good agreement with experimental observations of ZnO growth.